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The phosphaturic mesenchymal tumor of the craniofacial sinuses (mixed connective tissue variant) is an extremely rare, distinctive paraneoplastic syndrome that is frequently associated with oncogenic osteomalacia.
In this report is presented a case of 22 years old man indicated four years of progressive generalized pain and weakness, eventually becoming wheel-chair bound. His current presentation was for chest pain resulting from atraumatic rib fractures.
Imaging showed osteoporosis and multiple insufficiency fractures. CT and MRI showed an ethmoid mass. He had no symptoms referable to his nose or sinuses.
The ethmoid lesion was completely excised, the patient’s laboratory parameters returned to normal levels and the patient’s symptoms disappeared.
Phosphaturic mesenchymal tumor (PMT) is an uncommmon tumor that may cause oncogenic osteomalacia (1–6). This is due to an over expression of fibroblast growth factor-23 (FGF-23), a recently described protein capable of inhibiting renal tubular phosphate transport (6). Patients usually complain of a long history of bone pain and muscle weakness, often being so severely affected that they are unable to walk and become wheel-chair bound. We describe herein the radiological imaging and the clinic-pathologic features of a rare case of PMT which involved the craniofacial sinuses of the skull base.
A 22-year-old man who had been wheel-chair bound for one year and prone to atraumatic fractures for two years, was admitted to the hospital. The patient had no past medical history of note and no abnormality on physical examination. Laboratory investigations revealed hypophosphatemia, hyperphosphaturia, normocalcemia, normocalciuria, elevated alkaline phosphatase, and normal serum levels of parathormone and osteocalcin. Skeletal radiographs revealed homogeneus and fuzzy appearance due to the decline of contrast differences between bone marrow and calcified bone and bone scintigraphy findings were suggestive of osteomalacia. On computed tomography (CT) and magnetic resonance (MR) imaging, a tumor was discovered at the vault of the rhinopharynx, involving the ethmoid and sphenoid sinuses (Figures 11–5). The tumor was surgically removed. Histologically, the tumor was initially diagnosed as a perivascular myoid tumor and subsequently reclassified as a variant of a sinonasal hemangiopericytoma-like tumor (Figures 66–8). Immunostain for fibroblast growth factor FGF-23 protein was positive (Figure 9). Post-surgery, the patient’s metabolic disturbances persisted and further imaging revealed a residual tumor. A second surgical procedure was performed and with complete removal of the tumor, the patient’s laboratory parameters returned to normal levels and the symptoms disappeared.
We report a rare location of a PMT involving the craniofacial sinuses of the skull base. The typical laboratory findings secondary to phosphate loss are hypophosphatemia and hyperphosphaturia, which finally result in an inadequate mineralization of osteoid in mature bone, a metabolic disorder known as osteomalacia. Oncogenic osteomalacia is dramatically cured by tumor removal but when the tumor is not detected this condition can respond to 1,25 dihydroxyvitamin and phosphate supplementation. Phosphaturic mesenchymal tumor is usually located in soft tissue, but intraosseus as well sinonasal locations are also on record. Histologically, it corresponds to a polymorphous group of neoplastic entities (1–5), the most common of which is the so-called “mixed connective tissue type” (1–6), which is characterized by a distinctive admixture of bland spindled cells, osteoclast-like giant cells, microcysts, prominent and variously sized vasculature, smudgy to calcified cartilage-like matrix, and metaplastic bone. Other histological types of phosphaturic mesenchymal tumors are the osteoblastoma-like tumor, the non-ossifying fibroma-like tumor and the ossifing fibroblastoma-like tumor. Some cases have histological features of malignancy (6).
Phosphaturic mesenchymal tumor (PMT) is an uncommon, distinctive tumor that is frequently associated with oncogenic osteomalacia, itself a rare paraneoplastic syndrome. Sinonasal PMT is the rarest variant with its own peculiar histologic features, often differs from the mixed connective tissue type, and more closely resembles a sinonasal hemangiopericytoma-like variant (1). PMT is usually a benign tumor, but some cases of malignant transformation have been described (7). Metastatic disease has also been reported (malignant connective tissue variant) (7). Osteogenic osteomalacia – the clinical effect of the tumor – is vitamin D resistant, and is dramatically cured by tumor removal.
PMT is usually located in soft tissue, but intraosseous as well as sinonasal locations have also been reported. In Folpe et al.’s own series of PMT, 18 out of 32 total cases occurred in soft tissue, nine in bone and two in paranasal sinuses, including the present one (2). Patients are usually in their adulthood at the time of diagnosis, but pediatric cases have also been reported (age range: 5 to 63 years). Any site can be affected, with the lower extremities being the most common (40–50% of cases), followed by the head and neck area (15–20%), trunk (15–20%) and upper extremities (around 10%). Unusual locations (e.g. big toe) are not uncommon. Tumor size is variable, ranging from 1 cm to 15 cm, with a median size of 5.6 cm for soft tissue location (3, 4). Somatostatin receptor imaging has been recently proved to improve the detection of such tumors, based on the postulate that such tumors express somatostatin receptors (5).
In conclusion, PMT is a rare pathologic entity that is poorly understood by pathologists, clinicians and radiologists. PMT of craniofacial sinuses has peculiar histological features, which often differs from the mixed connective tissue type and which more closely resembles a sinonasal hemangiopericytoma-like tumor variant. Craniofacial PMT should be considered as a rare causative tumor in patients presenting with clinical and radiological features of oncogenic osteomalacia.
The Authors have disclosed any financial or conflict of interests.